Acrylic resin film obtained by processing and molding an acrylic resin composition containing a cross-linked elastomer is used in and developed for various applications for its transparency and hardness. Examples of the application of acrylic resin film include alternatives to painting to be laminated on interior or exterior car parts, exterior materials for mobile phones, personal computers and other home appliances, and floor materials for building. As a method for decorating a plastic surface, there is a film in-mold molding method in which a film, such as an acrylic resin film, previously subjected to or not subjected to vacuum molding or the like is inserted into an injection mold and a base resin is injected into the mold. Various acrylic resin films suitable for such an application have been proposed. For example, a method is known in which the reduced viscosity of a plastic polymer and the particle size and rubber content of a rubber-containing polymer are specified (Patent Document 1), and a method is known in which the reduced viscosity of an acrylic polymer and the amount of a multi-layer acrylic polymer contained are specified (Patent Documents 2 and 3). It is known that films obtained by these methods are excellent in surface hardness, transparency and film moldability.
In these Patent Documents, however, there is no description about the problem of film whitening on bending. These films for use in film in-mold molding each have a problem that when laminated on a molded article having a complicated shape, the film is likely to whiten due to the concentration of stress on the corners or the like of the molded article, which significantly reduces the commercial value of the molded article.
As a method for forming a film having improved resistance to whitening on bending, a method is known in which a relationship between the degree of cross-linking and particle size of a cross-linked elastomer is specified (Patent Document 4). However, a film formed by such a method has a problem that its resistance to whitening on bending is excellent but its balance of physical properties such as resistance to whitening on bending, cracking resistance and surface hardness is not optimized. Further, a method has been proposed in which two kinds of rubbers are blended to obtain an acrylic resin film having excellent solvent resistance and transparency (Patent Document 5). However, in Patent Document 5, there is no description about resistance to whitening on bending, and of course, there is no description about the balance of physical properties such as resistance to whitening on bending, cracking resistance, and surface hardness, either. Further, a method has been proposed in which two kinds of rubbers are blended to obtain an acrylic resin film that can maintain an excellent appearance without white turbidity even when heated during molding (Patent Document 6). However, also in Patent Document 6, there is no description about resistance to whitening on bending. Therefore, an improved balance of physical properties such as resistance to whitening on bending, cracking resistance, and surface hardness has not yet been achieved.
Patent Document 1: JP-A-8-323934
Patent Document 2: JP-A-10-279766
Patent Document 3: JP-A-10-306192
Patent Document 4: Japanese Patent No. 4291994
Patent Document 5: JP-A-2002-309059
Patent Document 6: Japanese Patent No. 3835275